My question pertains to pre-dawn Zodiacal light. Is this phenomenon visible when the Sun is at a constant negative altitude below the horizon? And whether other locations on higher latitudes will have that similar negative altitude? I've once observed this rare sight from my location 6deg south of the equator when the sun was 16.65deg below the horizon.

Zodiacal light is caused by sunlight reflecting off of dust in the ecliptic plane of our Solar System. Under ideal conditions, zodiacal light can be visible the entire night as a faint band of light following the zodiac across the sky. It brightens in the morning before sunrise, when the brighter band regions that are closer to the Sun rise above the horizon. However, when the Sun gets closer to the horizon, the sky begins to brighten, making it more and more difficult to see the faint zodiacal light behind the brightening sky. The best time to see this light will be when the Sun is between 18 and 12 degrees below the horizon, depending the local atmospheric conditions.

The zodiacal light is best seen close to the equator because the ecliptic rises at a steep angle to the horizon at any time of the year. From locations further from the equator, it can best be seen after sunset in the spring (i.e. April in the north and September in the south) and before sunrise in the fall.

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